III-V compound semiconductors such as InP have bandgap energies corresponding to the near-infrared to infrared region, and hence are studied for development of photodiodes for communications, biomedical examinations, image capturing at night, and the like. Absorption spectra of substances relating to living bodies and environments are in the near-infrared to infrared wavelength region. Therefore, expansion of sensitivity of the photodiodes using InP and the like to a long-wavelength region has been an important theme. For example, NON PATENT LITERATURE 1 proposes a mesa-type single-pixel photodiode including an absorption layer having an InGaAs/GaAsSb type-II multiple quantum well (MQW) structure on an InP substrate, in order to improve sensitivity in the long-wavelength region. In this photodiode, an InGaAs buffer is disposed on an InP substrate, and the InGaAs/GaAsSb type II multiple quantum well structure is disposed on the buffer. This mesa-type single-pixel photodiode has a cutoff wavelength of 2.39 μm. Sensitivity characteristics at wavelengths from 1.7 to 2.7 μm are demonstrated.
Meanwhile, a photodiode including an array of a plurality of pixels (absorption portions) is used in image pickup devices and the like. PATENT LITERATURES 1 and 2 each propose a planar photodiode in which pixels are formed by introducing an impurity by selection diffusion. In the photodiode, the above-mentioned InGaAs/GaAsSb type II multiple quantum well structure is used, and a semiconductor layered structure is appropriately modified to prevent the multiple quantum well structure from being deteriorated by the impurity. By using such a layered structure, it is possible to provide a photodiode including an array of pixels having sensitivity in the near-infrared to infrared region.
Meanwhile, NON PATENT LITERATURE 2 proposes LEDs and laser diodes having an emission wavelength of 2.14 μm, in which an InGaAs/GaAsSb type II MQW is formed as an active layer on an InP substrate. The type II MQW is grown at a temperature of 530° C. by metal-organic vapor phase epitaxy (MOVPE). As sources of InGaAs and GaAsSb, metal-organic gases thereof are disclosed.